The present invention relates generally to optical transmission networks and specifically to fault tolerance and recovery in Bi-directional Line Switched Ring (BLSR) types of Synchronous Optical Networks (SONET) employing Synchronous Digital Hierarchy (SDH).
Conventionally, BLSR networks can be one of either a 2-fiber BLSR or a 4-fiber BLSR types of SONET networks. The 2-fiber BLSR networks comprise a plurality of network equipment (“nodes”) interconnected by two optical fibers. On the other hand, in a 4-fiber BLSR network, nodes are interconnected by four optical fibers that provide a “working line” and a “protection line.”
Equipment faults and the like can cause obstacles to occur in a transmission. Such obstacles can block the path through the transmission line. One perceived drawback of conventional systems is that they do not presently provide remedies for obstacles and the like that can arise inside the node, which can sometimes disconnect a path through the node.
What is really needed are techniques for isolating a network node automatically in order to circumnavigate an obstacle occurring inside the node.